J. Prakt. Chemie 2, 51 (1895) page 148 and 149 describes the preparation of the compounds 1-methoxy-phthalazine and 1-ethoxy-phthalazine from 1-chlorophthalzaine and sodium methylate and sodium ethylate respectively.
U.S. Pat. No. 2,484,029 cites 1-phenoxy-phthalazine as starting substance for the preparation of 1-hydrazinophthalazine.
Neither of these references mentions that these compounds have pharmacological effects or renders these obvious.